Fabric and seam construction

ABSTRACT

A woven fabric comprises cross-machine direction weft yarns, and an array of interwoven warp yarns, the warp yarns being woven in the machine direction in alternating groups of relatively narrow yarns and relatively wide yarns. The narrow yarns are looped around a respective last weft yarn and backwoven, whilst the wider yarns are extended to form interdigitable loops for engagement of a pintle wire.

FIELD OF THE INVENTION

This invention relates to a woven fabric structure, partially in thefield of papermachine clothing and other industrial belting, andparticularly to structures contributing to the formation of a jointingseam in such a fabric for joining ends of the fabric to form an endlessbelt.

BACKGROUND OF THE INVENTION

A common form of seam is achieved by extending selected longitudinal(machine direction) warp yarns of the fabric beyond the last transverse(cross direction) weft yarn, to form a loop, the end of which isback-woven into the fabric. The non-selected machine direction warpyarns are looped about the last cross direction weft yarn and the endback-woven into the fabric. Such a structure is described inGB-A-1488815, which discloses two patterns of weaving back the loopedyarns, and cutting short of certain other MD yarns to provide space forthe back woven loop ends.

Normally all the warp yarns have the same thickness or width, so that asa result when using only half the warp-yarns to form the loops, toafford space for interdigitation of the corresponding loops of theopposite end of the fabric, the tensile strength of the seam isrelatively poor and there is a higher propensity in the seam region formarking of the paper sheet due to the greater open area in the seamregion, as about 50% of the total width of the fabric is open space.

One approach to solving this problem is to use more than 50% of the warpyarns to form the loops. An example of this is WO 92/15743 wherein theproblem of obtaining space for interdigitation of loops where more than50% space is used by the loops of each side, is tackled by crossingadjacent loops over each other. However the use of more than 50% warpyarns, and the crossing of the looped yarns makes the alreadycomplicated, prolonged and expensive seaming process take even longer tocarry out.

U.S. Pat. Nos. 5,503,196 and 5,769,131 describe a warp yarn system in apapermakers fabric comprising single wide tape-like yarns alternatingwith pairs of narrow yarns. The wide yarns are disposed with long floatsand form an outer shell to protect the woven structure. These wide tapelike yarns are, in U.S. Pat. No. 5,503,196 explicitly not used forseaming whilst U.S. Pat. No. 5,769,131 shows wide yarns from one fabricend being interdigitated with narrow yarns from the other fabric end,and the wide yarns are not used for seaming from both ends of thefabric.

SUMMARY OF THE INVENTION

An object of the invention is to provide a fabric structure whichenables seaming to be carried with more than 50% of the warp yarn width,thus attaining lower open space in the seam, leading to a reducedpropensity to marking of the paper sheet.

According to the invention a woven fabric structure comprises an arrayof warp yarns interwoven with an array of substantially orthogonallyextending weft yarns using warp yarns of differing width, characterisedin that said warp yarns comprise relatively wide warp yarns arranged ingroups of two or more alternatively with relatively thin warp yarnsarranged in groups of two or more and that said relatively wide warpyarns are extended in a seam region to provide seaming loops on each endof the fabric.

The fabric is preferably for papermachine clothing, such as a dryerfabric a forming fabric, extending nip press belt, press sleeve,basecloth, or for a filter belt or conveyor belt.

The warp yarns are preferably arranged in groups comprising alternatingpairs of relatively wide yarns and pairs of relatively thin yarns. Thealternating groups of warp yarns may each comprise single yarns, or anyother number, and need not comprise the same of wider and thinner yarnsin the respective groups.

In seaming the fabric, in order to effect a loop and pintle wire joiningseam between the opposite ends of the fabric, the thinner yarns arepreferably looped around the last weft yarn (extending parallel to theedge, across the width of the fabric), and the wider yarns are extendedbeyond the last weft yarn to form loops which are interdigitated withsimilar loops of the opposing fabric end, and joined by a pintle wirepassed through the tunnel formed by the interdigitated loops.

The loops will, being provided by the wider yarns, comprise more than50% of the width of the fabric.

The fabric may comprise a single layer woven construction, with all weftyarns in a single tier, however multi layer, or multi-weft tier fabricsmay also be used.

The warp yarns, at least the wider yarns, are preferably flat yarns. Thethinner yarns may also be flat yarns. However either or both the widerand thinner warp yarns may be of other cross-sectional profiles, such astriangular or semi-circular.

The invention also provides a method of seaming a woven fabric forforming the fabric into an endless belt the fabric being formed with anarray of longitudinally extending warp yarns of differing widths,characterised in that the warp yarns comprise relatively wide yarnsarranged in groups of two or more alternatively with relatively thinwarp yarns arranged in groups of two or more, said relatively thin warpyarns being looped about a last weft yarn of the fabric edge, and therelatively wide warp yarns being formed into extended loops extending inthe plane of the fabric beyond said last weft yarn at both ends of thefabric.

Preferably the seam is completed by interdigitating said loops withcorresponding loops on an opposed end of the fabric, and passing apintle or wire through said interdigitated loops.

The invention further provides an endless fabric formed by seaming bythe method according to the invention, or comprising a fabric includinga woven fabric structure according to the invention.

DESCRIPTION OF THE DRAWINGS

A preferred embodiment of fabric structure, seam, seaming method andendless fabric according to the invention will now be described by wayof example with reference to the accompanying drawings wherein likereferenced numerals refer to like parts and wherein:

FIG. 1 is a fragmentary enlarged detail view of part of a seam edgeregion of a woven papermachine fabric, showing part of the weavestructure of the fabric of the seam formation;

FIGS. 2a to 2 c are cross-sectional views of yarn cross-sections used inthe fabric; and

FIG. 3 is a diagram of an endless belt formed by the seamed fabric ofthe invention.

In FIG. 1, a woven fabric for a papermachine or other belt comprises.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The wider and thinner yarns may be grouped in numbers other than pairs,from single yarns up, and the groups of wider and thinner yarns maycomprise different numbers of yarns, e.g. 1 and 2, or 2 and 3.

In an example similar to FIG. 1, a seam with 75% cover, ie 25% open areawas made using flat warp (MD) yarns measuring 0.27×39 mm and0.27(height)×0.75 mm(width). For every set of 4 warp yarns, two arewide, and are used to form seam loops 14. The seam strength was measuredat 43 kg/cm, compared with 32 kg/cm for a fabric containing 56% warpcover if 4 narrow warp yarns are used in each set. These figures applyto a fabric with a warp density of 188 ends per 10 cm, woven to allow 6%reed width, and following heat setting has a warp density of 200 ends/10cm.

As shown in FIG. 2, the yarns, particularly the wider yarns 12 may haveany of a number of cross-sectional profiles, such as flattened (FIG.2a), circular (FIG. 2b) or elliptical (FIG. 2c).

The weave structure and seamed fabric belt of the invention can be inany appropriate application as papermachine clothing, as a filter belt,or conveyor belt or the like. The fabric may constitute a base for afurther layer or layers such as fibrous non-woven batts etc, filtrationcoatings etc, depending upon the intended use of the belt.

The narrow yarns 11, may be of equal height to the yarns 12, as shown inFIG. 2a to form a mono-planar sheet support surface, or may be of thesame proportions, and thus lower than the wide yarns as in FIGS. 2b and2 c. This latter arrangement is desirable when a ribbed dryer fabric isrequired, such ribs may be provided on the sheet side or the machineside of the fabric. The ribs and grooves in one end of the fabric arepreferably aligned with these on the other end the fabric on theopposite side across the seam. Ribbed fabrics can also be used to embossthe sheet, for example as a tissue forming or drying fabric, or toprovide yarns standing proud to provide extra resistance to wear.

The seam construction can be used to make an endless forming fabric orpress felt, or base cloth.

What is claimed is:
 1. A woven fabric structure comprising an array ofmachine direction yarns interwoven with an array of substantiallyorthogonally extending cross machine direction yarns using machinedirection yarns of differing widths, said machine direction yarnscomprising groups of relatively wide machine direction yarns and groupsof relatively thin machine direction yarns, said groups of relativelywide machine direction yarns alternating with said groups of relativelythin machine direction yarns, said groups of relatively wide and ofrelatively thin machine direction yarns each including one or more wideor thin machine direction yarns respectively, wherein said relativelywide machine direction yarns are extended into a seam region to provideseaming loops on each end of the fabric structure.
 2. The fabricstructure according to claim 1 wherein at each end of the fabric thegroups of relatively thin machine direction yarns are looped around thelast cross machine direction yarn, and the groups of relatively widemachine direction yarns are extended beyond said last cross machinedirection yarn to form loops, which can be interdigitated with similarloops of the opposing fabric end and joined by a pintle wire passedthrough a tunnel formed by the interdigitated loops.
 3. The fabricstructure according to claim 2 wherein the extended loops comprise morethan 50% of the width of the fabric.
 4. The fabric structure accordingto claim 1 wherein the relatively wide machine direction yarns are flatyarns.
 5. The fabric according to claim 1 wherein either or both of thewider and thinner machine direction yarns are of a triangular orsemicircular cross-section.
 6. A method of seaming a woven fabric toform the fabric into an endless belt, comprising forming the fabric withan array of longitudinally extending machine direction yarns ofdiffering widths by arranging relatively wide machine direction yarns ingroups of one or more alternately with groups of one or more relativelythin machine direction yarns, looping said relatively thin machinedirection yarns about a last cross direction yarn of the fabric edge,and extending the relatively wide machine direction yarns into a seamregion to form extended seaming loops extending in the plane of thefabric beyond said last cross direction yarn at both ends of the wovenfabric.
 7. The method according to claim 6 further comprising completingthe seam by interdigitating said loops with corresponding loops on theopposed end of the fabric and passing a pintle wire through saidinterdigitated loops.
 8. An endless fabric formed by seaming a fabrichaving a structure comprising an array of machine direction yarnsinterwoven with an array of substantially orthogonally extending crossmachine direction yarns using machine direction yarns of differingwidths, said machine direction yarns comprising groups of relativelywide machine direction yarns and groups of relatively thin machinedirection yarns, said groups of relatively wide machine direction yarnsalternating with said groups of relatively thin machine direction yarns,said groups of relatively wide and of relatively thin machine directionyarns each including one or more wide or thin machine direction yarnsrespectively, wherein said relatively wide machine direction yarns areextended into a seam region to provide seaming loops on each end of thefabric structure.
 9. The endless belt formed by the method of claim 6.